Measuring devices using retractable coiled flexible tapes mounted inside a housing are well known in the art. A common type of such a measuring device has a housing having a slot. A flexible tape having measuring indicia thereon is coiled around a reel mounted inside the housing with a free end of the flexible tape extending through the slot. A retraction mechanism, typically a coil spring, acts upon the reel biasing the flexible tape in the retracted position. In use, a user pulls enough of the flexible tape from the housing through the slot to make the desired measurement using the indicia located on the flexible tape. When the user has completed making the measurement, the flexible tape is rewound onto the reel and stored inside the housing. Such common retractable flexible tape measuring devices are found in many toolboxes around the world.
Over the years, many variations of the basic flexible retractable tape measuring device have been made.
An example is seen in U.S. Pat. No. 6,276,071, Khachatoorian, Tape Measure With Tape Breaking Control Mechanism, discloses a spring-loaded tape cartridge in a tape measure including a coilable tape rotatably mounted to position a free end of the tape to pass through an opening in the housing. The tape cartridge is biased to retract the tape into the compartment when the free end is pulled out of the housing to perform a measurement. A stop tab at the free end engages the workpiece and assures that the free end remains outside the housing and available for gripping. An internal spring portion acts between the housing and the tape cartridge for applying a substantially constant frictional force on the tape cartridge. This particular measuring device has a second spring portion for selectively applying increased and decreased frictional forces on the tape cartridge to supplement the substantially constant frictional force. A locking member is provided for selectively applying a substantially normal pressure to the tape, transverse to the movement path, to positively lock the tape against the housing and prevent the tape from moving relative to the housing.
U.S. Pat. No. 6,349,482, Gilliam, Three Position Locking Mechanism For a Tape Measure, discloses a retractable tape measure having a flexible tape biased in a coiled position and a housing to contain the flexible tape. The flexible tape (20) is coiled around one shaft (24). A tape biasing device (40) is mounted within the housing using a spring (42) strung between two separate shafts (see 44 and 46) separate from the axis of the flexible tape (20). The tape measure also includes a locking mechanism (50).
U.S. Pat. No. 5,119,521, Clontz, Tape Measure for Hand Tools, discloses a tape measure frame assembly for installation within the handle of a hand tool. The assembly includes a gearing connection between the tape and a retracting spring, which enables the assembly to be elongated in conformity with the tool handle. Coiled spring (12) is wrapped in two coils (12A and 12B) around shafts (16 and 15, respectively). Flexible tape (T) is wrapped around a single rotatable shaft (20).
U.S. Pat. No. 5,414,943, Vogt, Anatomical Measuring Tape With Indicator, discloses a measuring device with a different twist. The measuring device has two measuring tapes held on separate reels in a housing. The housing has two windows for displaying measurement indicia appearing on each tape. The tapes are spring biased toward the fully wound condition. The two tapes contained within one housing are held on separate reels and operate independently. Each tape is held on a single reel.
U.S. Pat. No. 5,832,622, Mann, Direct Reading Inside and Outside Tape Measure, discloses a measuring tape which allows both inside and outside dimensions to be read directly from the same printed face of the tape. The tape measure has a case having a tape coiled inside the case and extending out of the case through a slot in the case. Inside the case is a guide wheel which guides the tape along a bottom wall of the case. The front wall of the case is transparent so that the graduations on the tape can be seen adjacent to the bottom wall. A pointer on the case points to the graduations such that when the tape is fully retracted, the pointer points to a measurement corresponding to the width of the case. This enables the case and the tape to be used to make inside measurements. Flexible measuring tape (20) is wound around single reel (24) inside the case to form a coil. A separate wheel (34) is fixed on shaft (32) which forces tape (20) near wall (22) as tape (20) is unwound from reel (24) around which tape (20) is stored.
It is also desirable to be able maximize the length of measurement which can be taken with the flexible tape measuring device. This can be done by increasing the length of the flexible tape stored within the housing. However, since a given flexible tape has a finite thickness, the more tape that is wrapped around the storage reel inside the housing, the greater the diameter of the wound reel. The greater the diameter of the wound, the greater the overall size of the housing must be. Not only does the an increased housing size take up more space in a tool box, but, more importantly, the larger the measuring device in the hand of the user, the more difficult that it is to hold comfortably and reliably. Thus, common flexible tape measuring devices have a realistic maximum amount of flexible tape that can be reasonably stored within the housing based upon the thickness of the flexible tape and a required maximum housing size for comfortable and reliable use. While flexible tapes possibly can be made thinner allowing more tape to be held on the reel, a thinner tape usually does not perform as well in taking measurements. It is desirable to have a flexible tape which is thick enough to have some rigidity so it is easier for one person to make a measurement. Thus, thinner tape is not the answer either.